Quarterly Results (Summarized Quarterly Results Of Operations) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Quarterly Results [Abstract]
Interest income	$ 63,981	$ 62,949	$ 63,194	$ 53,254	$ 51,042	$ 40,725	$ 47,769	$ 60,242	$ 243,378	$ 199,778	$ 314,595
Interest expense	(17,743)	(17,930)	(15,894)	(14,513)	(14,081)	(13,282)	(13,333)	(15,555)	(66,080)	(56,251)	(128,830)
Net interest income (expense)	46,238	45,019	47,300	38,741	36,961	27,443	34,436	44,687	177,298	143,527	185,765
Other revenue (expense)	(4,335)	(4,080)	(4,824)	(4,114)	(3,999)	(3,834)	(4,742)	(4,315)	(17,353)	(16,890)	(56,761)
Equity in earnings of unconsolidated affiliates	65	64	65	65	65	64	65	65	259	259	259
Net income	$ 41,968	$ 41,003	$ 42,541	$ 34,692	$ 33,027	$ 23,673	$ 29,759	$ 40,437	$ 160,204	$ 126,896	$ 129,263
Basic and diluted net income per common share	$ 0.43	$ 0.43	$ 0.48	$ 0.41	$ 0.40	$ 0.27	$ 0.35	$ 0.51